1. Field of the Invention
The present invention relates generally to fully human monoclonal antibodies, method of making same, and their use in preventive and therapeutic applications for anthrax. In one aspect, antibodies that have binding specificity for anthrax protective antigen (PA) toxin are provided.
2. Description of the Related Art
Anthrax is a zoonotic soil organism endemic to many parts of the world. The Bacillus anthracis organism was one of the first biological warfare agents to be developed and continues to be a major threat in this regard. The Centers for Disease Control and Prevention (CDC) has emphasized that the United States faces a new wave of terrorism, in the form of a biological attack. For example, in late 2001, Bacillus anthracis spores were intentionally distributed through the postal system, causing 22 cases of anthrax, including 5 deaths. Anthrax is a key toxin that can be employed by terrorists to debilitate a nation.
Although vaccine strains have been developed for anthrax, currently there are concerns regarding their efficacy and availability. After inhalation by mammals, Bacillus anthracis spores germinate in the alveolar macrophages, then migrate to lymph nodes where they multiply and enter the bloodstream. The vegetative bacteria excrete the tripartite exotoxin that is responsible for the etiology of the disease. Virulent strains of Bacillus anthracis secrete a set of three distinct antigenic protein components: protective antigen (PA), edema factor (EF), and lethal factor (LF). PA can bind either LF or EF, forming lethal toxin (LeTx) or edema toxin (EdTx). Collectively these two toxins are seen as a complex exotoxin called anthrax toxin. Each component of the toxin is a thermolabile protein with a molecular weight exceeding 80 kDa. EF is a calmodulin dependent adenylate cyclase that is responsible for the edema seen in anthrax infections. LF is a zinc-metalloprotease that is needed for the lethal effect of the anthrax toxin on macrophages. It is believed that PA contains the binding domain of anthrax toxin, which binds to recently identified receptors on the cell surface called collectively anthrax toxin receptors (ATRs) and allows translocation of LF or EF into the cell by endocytosis.
Evidence that the hu-PBL-SCID system (severe combined immunodeficient (SCID) mice engrafted with human peripheral blood leukocytes) can be used to obtain recall antibody responses dates from the original publication of the method by Mosier and co-workers. Mosier et al., Nature 335:256 (1988), herein incorporated by reference. In that report, tetanus toxoid was administered to human PBL engrafted mice, and human antibodies to tetanus were found in the serum post-immunization. Since this original report, many investigators have used the hu-PBL-SCID system to examine aspects of the human recall antibody response to multiple antigens. See, for example, Nonoyama, S. et al., J. Immunol., 151:3894 (1993); Walker, W. et al., Eur. J. Immunol., 25:1425 (1995); Else, K. J., and Betts. C. J., Parasite Immunology 19:485 (1997), all herein incorporated by reference. However, reports describing the generation of useful monoclonal antibodies from such engrafted mice have been sporadic. Duchosal, M. A. et al., Letters To Nature:258 (1991); Satoh, N. et al., Immunology Letters 47:113 (1995); Uchibayashi, N. et al., Hybridoma 14:313 (1995). Nguyen, H. et al., Microbiol. Immunol. 41:901 (1997); Coccia, M. A and P. Brams, Amer. Assoc. Immunologists:5772 (1998); and Smithson, S. L. et al., Molecular Immunology 36:113 (1999), all herein incorporated by reference.